Circuit device and method of manufacturing the same

ABSTRACT

In a circuit device of the present invention, the lower surface side of a circuit board and part of side surfaces thereof are covered with a second resin encapsulant, and the upper surface side and the like of the circuit board are covered with a first resin encapsulant. Since heat dissipation to the outside of the circuit device is achieved mainly through the second resin encapsulant, a particle size of filler contained in the second resin encapsulant is made larger than a particle size of filler contained in the first resin encapsulant. Heat dissipation to the outside of the circuit device is greatly improved.

This application claims priority from Japanese Patent Application NumberJP 2010-164996 filed on Jul. 22, 2010, the content of which isincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a circuit device which improves theheat dissipation of a resin package, and a method of manufacturing thesame.

2. Description of the Related Art

As one example of a conventional method of manufacturing a circuitdevice, the following manufacturing method has been known. As shown inFIG. 9A, a circuit board 71 made of a metal substrate such as an Alsubstrate is prepared, and an insulative resin layer 72 and a conductivepattern 73 are formed on an upper surface of the circuit board 71.Further, circuit elements 74 and leads 75 are electrically connected tothe top of the conductive pattern 73 to form a hybrid integrated circuiton the circuit board 71. Then, the circuit board 71 is placed in acavity 77 of a resin encapsulation mold 76, and the leads 75 are clampedbetween an upper mold half 78 and a lower mold half 79. Thus, thecircuit board 71 is fixed in the cavity 77.

As shown in FIG. 9B, resin is injected into the cavity 77 through a gateportion 80 of the resin encapsulation mold 76. At this time, asindicated by an arrow 81, the injected resin collides against a sidesurface of the circuit board 71 first. The resin flows to the upper andlower surface sides of the circuit board 71 as indicated by arrows 81Aand 81B. Further, a curved surface 82 is disposed at an edge portion ofthe lower surface of the circuit board 71, and therefore the resin isallowed to efficiently flow to the lower surface side of the circuitboard 71. Although the thickness of a resin encapsulant under the lowersurface of the circuit board 71 is, for example, approximately 0.5 mm,the aforementioned resin injecting method enables the narrow gap to befilled with the resin. This technology is described for instance inJapanese Patent Application Publication No. 2003-17515 (pages 6 to 9,and FIGS. 8 and 9).

Moreover, as one example of a conventional circuit device, the followingstructure has been known. As shown in FIG. 10, in a circuit device 91, ahybrid integrated circuit including a conductive pattern 93 and circuitelements 94 is constructed on an upper surface of a circuit board 92,and the upper, side, and lower surfaces of the circuit board 92 areintegrally covered with a resin encapsulant 95. Further, the resinencapsulant 95 includes a first resin encapsulant 95A formed by transfermolding and a second resin encapsulant 95B formed by melting a solidresin sheet. It should be noted that as shown in the drawing, from sidesurfaces of the resin encapsulant 95, leads 96 electrically connected tothe conductive pattern 93 on the upper surface of the circuit board 92are led out of the resin encapsulant 95. This technology is describedfor instance in Japanese Patent Application Publication No. 2010-67852(pages 4 to 10, and FIGS. 1 to 4).

First, in the manufacturing method described with reference to FIGS. 9Aand 9B, the resin injected through the gate portion 80 of the resinencapsulation mold 76 collides against a side surface of the circuitboard 71, and the utilization of the curved surface 82 formed in thecircuit board 71 makes it easy to fill a narrow region under the lowersurface of the circuit board 71 with the resin. Further, to prevent theformation of an incompletely filled region in the narrow region underthe lower surface of the circuit board 71, a width enough to allow theflow of the resin is needed. Thus, there is the problem that it isdifficult to realize a reduction in the thickness of the resinencapsulant under the lower surface of the circuit board 71, and toimprove the heat dissipation from the resin encapsulant.

In particular, conceivable ways to solve this problem of heatdissipation include increasing the filler content in resin forencapsulation and increasing the particle size of the filler. However,increasing the filler content or increasing the particle size thereofcauses another problem that the flowability of the resin deteriorates tomake an incompletely filled region more likely to be formed under thelower surface of the circuit board 71. Furthermore, with regard to thematerial and shape of the filler used, manufacturing methods in whichall the surfaces of the circuit board 71 are integrally encapsulated ina single type of resin also have problems such as damage to circuitelements and breakage of fine metal wires, thus having the problem thatthe material and shape thereof are limited.

Next, in the circuit device 91 described with reference to FIG. 10,though an incompletely filled region is prevented from being formedunder the lower surface of the circuit board 92, and a reduction in thethickness of the resin encapsulant is realized, no disclosure is madewith regard to a structure for further improving heat dissipation.

Moreover, a region indicated by a circle 97 represents a polymerizedregion of the first resin encapsulant 95A and the second resinencapsulant 95B. As shown in the drawing, the second resin encapsulant95B is formed to extend to the side surfaces of the circuit board 92 tosuch an extent to cover a lower end portion of the circuit board 92.Further, the polymerized region is prone to have a lower withstandvoltage characteristic than single-material regions of the respectivefirst and second resin encapsulants 95A and 95B. Accordingly, there isthe problem that the circuit board 92 is short-circuited through thepolymerized region when the polymerized region is located under thelower surface of the circuit board 92 or on lower portions of the sidesurfaces of the circuit board 92.

Further, if a reduction in the thickness of the second resin encapsulant95B is realized to improve the heat dissipation of the circuit device91, the percentage of the film thickness of the first resin encapsulant95A to the thickness of the entire resin encapsulant 95 increases.Accordingly, there is the problem that the circuit board 92 is prone towarpage due to the shrinkage force of first resin encapsulant when thefirst resin encapsulant 95A is thermally cured in the resinencapsulation mold.

SUMMARY OF THE INVENTION

The present invention has been made in view of the aforementionedcircumstances. A circuit device of the present invention is a circuitdevice including a circuit board, a conductive pattern provided on theside of one main surface of the circuit board, a circuit element fixedon the conductive pattern, and a resin encapsulant covering the circuitboard. The circuit board has the one main surface, other main surfaceopposite to the one main surface, and a side surface located between theone main surface and the other main surface. The resin encapsulantincludes a first resin encapsulant covering at least the side of the onemain surface of the circuit board and part of the side surface thereofand a second resin encapsulant covering at least the side of the othermain surface of the circuit board and part of the side surface thereof.A polymerized region of the first resin encapsulant and the second resinencapsulant is located to extend beside the side surface of the circuitboard, and a top portion of the polymerized region is located at aposition lower than the side of an upper surface of the circuit board.

Moreover, a method of manufacturing a circuit device of the presentinvention is a method of manufacturing a circuit device in which acircuit board having a circuit element disposed on the side of one mainsurface thereof is placed in a resin encapsulation mold and in which afirst encapsulating resin is injected into a cavity of the resinencapsulation mold to form a resin encapsulant. The method includes thesteps of preparing a resin sheet formed by pressing a powdery resinmaterial containing a thermosetting resin and placing the resin sheet inthe cavity of the resin encapsulation mold so that the circuit board maybe mounted on the resin sheet, and forming the resin encapsulant in sucha manner that, the second encapsulating resin covers the side of othermain surface of the circuit board, which is opposite to the one mainsurface, and part of a side surface of the circuit board, which islocated between the one main surface and the other main surface, and thefirst encapsulating resin injected into the cavity covers the side ofthe one main surface of the circuit board and part of the side surfaceof the circuit board, while the first encapsulating resin and the secondencapsulating resin are polymerized beside the side surface.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are a perspective view and a cross-sectional view forexplaining a circuit device in an embodiment of the present invention,respectively.

FIGS. 2A and 2B are a perspective view and a cross-sectional view forexplaining the circuit device in the embodiment of the presentinvention, respectively.

FIGS. 3A to 3C are cross-sectional views for explaining a method ofmanufacturing a circuit device in an embodiment of the presentinvention.

FIGS. 4A and 4B are cross-sectional views for explaining the method ofmanufacturing a circuit device in the embodiment of the presentinvention.

FIGS. 5A and 5B are a plan view and a cross-sectional view forexplaining a semiconductor device in an embodiment of the presentinvention, respectively.

FIGS. 6A and 6B are plan views for explaining a method of manufacturinga semiconductor device in an embodiment of the present invention.

FIGS. 7A to 7C are cross-sectional views for explaining the method ofmanufacturing a semiconductor device in the embodiment of the presentinvention.

FIGS. 8A and 8B are cross-sectional views for explaining the method ofmanufacturing a semiconductor device in the embodiment of the presentinvention.

FIGS. 9A and 9B are cross-sectional views for explaining a circuitdevice in a conventional embodiment and a method of manufacturing thesame.

FIG. 10 is a cross-sectional view for explaining a circuit device in aconventional embodiment.

DESCRIPTION OF THE INVENTIONS

Hereinafter, a circuit device according to a first embodiment of thepresent invention will be described. FIG. 1B is a cross-sectional viewof a circuit device shown in FIG. 1A, which is taken along line A-A.FIG. 2A is a perspective view for explaining a resin sheet. FIG. 2B is across-sectional view for explaining the resin sheet.

FIG. 1A shows a perspective view of a circuit device 1. In the circuitdevice 1, a hybrid integrated circuit including a conductive pattern 6(see FIG. 1B) and circuit elements is constructed on an upper surface ofa circuit board 4 (see FIG. 1B) in a resin encapsulant 2, and leads 3connected to this circuit are led out of the resin encapsulant 2.Further, the upper, side, and lower surfaces of the circuit board 4 arecovered with the resin encapsulant 2 made of a thermosetting resin.

As shown in FIG. 1B, the circuit board 4 is a substrate made of metalsuch as aluminum or copper, and has, for example, a shape in whichlength×width×thickness=approximately 61 mm×42.5 mm×1.5 mm. Here, amaterial other than metal may be employed as the material of the circuitboard 4. For example, a ceramic or a resin material may be employed.

An insulating layer 5 is formed to cover the entire region of a surfaceof the circuit board 4. The insulating layer 5 is made of an epoxy resinhighly filled with filler. Further, the conductive pattern 6 is formedsuch that a predetermined circuit is realized on the upper surface ofthe insulating layer 5. The conductive pattern 6 is made of a metal filmof, for example, copper or the like, and the thickness thereof isapproximately 50 μm.

A semiconductor element 7 and a chip element 8 constituting the circuitelements are fixed at predetermined positions on the conductive pattern6 with an adhesive 9 such as solder. Further, the semiconductor element7 and the conductive pattern 6 are connected through fine metal wires10. Here, a transistor, an LSI chip, a diode, or the like is employed asthe semiconductor element 7. A chip resistor, a chip capacitor, or thelike is employed as the chip element 8. It should be noted that as shownin the drawing, a heat sink may be disposed between the semiconductorelement 7 and the conductive pattern 6.

The leads 3 are fixed to pads 11 provided in a peripheral portion of thecircuit board 4, and function as external connection terminals throughwhich input signals and output signals pass. Further, as shown in FIG.1A, a large number of leads 3 are disposed along two opposite side edgesof the circuit board 4 in the longitudinal direction. It should be notedthat the pads 11 constitute part of the conductive pattern 6.

The resin encapsulant 2 includes a first resin encapsulant 2A and asecond resin encapsulant 2B. A region indicated by circles 12 is apolymerized region (region in which resins are mixed and in whichsufficient bonding strength can be obtained) of the first resinencapsulant 2A and the second resin encapsulant 2B, and the resinencapsulants 2A and 2B are integrated in this region. This polymerizedregion is a region in which a withstand voltage characteristic tends tobe slightly lower than a region in which the first resin encapsulant 2Aor the second resin encapsulant 2B is singly formed. Further, in thecase where this polymerized region is located on the lower surface sideof the circuit board 4 and in the vicinities of lower end portions ofthe side surfaces thereof, and where the circuit device 1 is mounted onthe upper surface of a heat sink, the circuit board 4 and the heat sinkare short-circuited through this polymerized region.

Accordingly, in this embodiment, this polymerized region is locatedabove the centers of the side surfaces of the circuit board 4. Thus, thecircuit board 4 is prevented from being short-circuited to externalmembers through this polymerized region. Moreover, as indicated by thecircles 12, the second resin encapsulant 2B on the side surfaces of thecircuit board 4 is cured to protrude toward the upper surface side ofthe circuit board 4. Further, the size and thickness of a resin sheet 13are adjusted so that a top portion 12A of the second resin encapsulant2B may be lower than the upper surface (including the surface of theinsulating layer 5) of the circuit board 4. This structure prevents theresin constituting the second resin encapsulant 2B from moving around tothe upper surface side of the circuit board 4, and prevents the moistureresistance on the upper surface side of the circuit board 4 from beingdeteriorated by alumina contained in the resin. Further details will bedescribed later. Moreover, the size and shape of alumina prevent damageto the circuit elements and breakage and the like of fine metal wires.

Further, the first resin encapsulant 2A is formed by injecting meltedresin into a cavity of a resin encapsulation mold. The first resinencapsulant 2A covers the circuit elements such as the semiconductorelement 7, connecting portions of the leads 3, and the upper surface andpart (upper portion of the circuit board 4) of the side surface of thecircuit board 4.

On the other hand, the second resin encapsulant 2B is formed by meltingthe resin sheet 13 (see FIG. 2A) placed under the lower surface of thecircuit board 4. The second resin encapsulant 2B covers the lowersurface of the circuit board 4, and further covers to upper portions,which are indicated by the circles 12, of the side surfaces of thecircuit board 4. Further, the second resin encapsulant 2B under thelower surface of the circuit board 4 has a thickness T1 of, for example,not less than 0.1 mm nor more than 0.3 mm to form a very thin film.Moreover, the second resin encapsulant 2B at the side surfaces of thecircuit board 4 also has a thickness T2 of, for example, not more than1.0 mm to form a thin film. Since the second resin encapsulant 2Bcontains alumina, which has excellent thermal conductivity, and hassmall thicknesses T1 and T2 to form a thin film, the thermal resistancein the second resin encapsulant 2B is reduced. Further details will bedescribed later. Further, heat radiated from the circuit elements suchas the semiconductor element 7 is favorably radiated outside the circuitdevice 1 through the circuit board 4 and the second resin encapsulant2B.

As shown in FIG. 2A, the resin sheet 13 is formed in the shape of asheet by molding a granular, powdered resin having a thermosetting resinas the main ingredient thereof by compression molding (tableting). Anepoxy resin, ortho-cresol novolac/biphenyl, dicyclopentadiene, or thelike is employed as the powdered resin. Further, filler is mixed in thepowdered resin. With regard to the type of the filler, alumina isemployed. Crystalline silica, crushed silica, fused silica, or siliconnitride may be employed to be mixed with alumina.

The two-dimensional size (L1×L2) of the resin sheet 13 depends on thetype of the circuit device 1 in which the resin sheet 13 is used. Theresin sheet 13 has a size similar to that of the circuit board 4 to beused or is slightly larger than the circuit board 4. On the other hand,the thickness T3 of the resin sheet 13 is, for example, not less than0.1 mm nor more than 0.8 mm.

As shown in FIG. 2B, the resin sheet 13 is made of a powdered resin 14including a large number of particles. This powdered resin 14 is made ofa thermosetting resin, such as an epoxy resin, which has an additivesuch as filler added thereto. The diameter of each particle of thepowdered resin 14 is, for example, not more than 1.0 mm. Further, in theresin sheet 13, the packing fraction (the fraction of the space occupiedby the powdered resin 14 in the total volume of the resin sheet 13) ofthe powdered resin 14 is not less than 99%. Thus increasing the packingfraction of the resin sheet 13 reduces the occurrence of voids in thesecond resin encapsulant 2B formed by the melting of the resin sheet 13.

As described previously, first, the first resin encapsulant 2A is formedby injecting melted resin into the cavity of the resin encapsulationmold. Further, it is necessary to prevent the hard filler contained inthe resin from colliding against the circuit elements and the fine metalwires at the time of resin injection and causing damage to the circuitelements and wire sweep and breakage of the fine metal wires.Accordingly, spherical filler is used as the filler contained in theresin which forms the first resin encapsulant 2A, and the particle sizethereof is up to approximately 75 μm.

Further, the first resin encapsulant 2A mainly covers the upper surfaceside of the circuit board 4, and is required to have moisture resistancefor the purposes such as the prevention of corrosion of the fine metalwires rather than heat dissipation. Accordingly, silica, which hasexcellent moisture resistance, is used as the filler. Since thematerials cost of silica is inexpensive compared to that of alumina,materials cost is reduced while ensuring the moisture resistance of thefirst resin encapsulant 2A. It should be noted that in the first resinencapsulant 2A, since importance is placed on moisture resistance, thefiller content can also be reduced. In this case, the hard filler lessfrequently collides against the circuit elements and the fine metalwires at the time of resin injection. Thus, damage to circuit elementsand the like are reduced.

Next, the second resin encapsulant 2B is formed by melting the resinsheet 13. The circuit board 4 sinks into the resin of the melted resinsheet 13, causing the second resin encapsulant 2B to cover the lowersurface side of the circuit board 4. Further details will be describedlater. In other words, unlike the first resin encapsulant 2A, the resinforming the second resin encapsulant 2B does not need to flow through agap of, for example, approximately 0.3 mm between the lower surface ofthe circuit board 4 and an inner wall of a lower mold half 22.Accordingly, filler having a particle size of up to approximately 150 μmis used as the filler contained in the resin forming the second resinencapsulant 2B. In other words, in the second resin encapsulant 2B,since filler having a larger particle size than that of the first resinencapsulant 2A is used, the thermal resistance in the second resinencapsulant 2B is greatly reduced, and heat dissipation from the lowersurface side of the circuit board 4 is greatly improved. It should benoted that since the resin forming the second resin encapsulant 2Bhardly flows at all as described previously, the entire region of thesecond resin encapsulant 2B is relatively uniformly filled with thefiller. This structure makes the thermal resistance of the second resinencapsulant 2B uniform over the entire region thereof.

Further, the second resin encapsulant 2B is intended to mainly coverfrom the lower surface side of the circuit board 4 to an upper portionof the side surfaces thereof, and is formed not to move around to theupper surface side of the circuit board 4. Accordingly, as describedpreviously, no consideration needs to be given to problems such asdamage to the circuit elements and breakage of the fine metal wires, andfiller having a polygonal shape such as crystalline filler or crushedfiller is used as the filler. Since the filler shape is a polygonalshape, the surface area of the filler increases, the contact areabetween the filler and the resin increases, thermal conductivity throughthe filler becomes favorable, and the thermal resistance in the secondresin encapsulant 2B is greatly reduced. This structure realizesexcellent heat dissipation not only from the lower surface side of thecircuit board 4 but also from the side surface side thereof in thecircuit device 1, and greatly improves the total heat dissipation of thecircuit device 1. It should be noted that increasing the amount of thefiller contained in the second resin encapsulant 2B to an amount largerthan that of the filler contained in the first resin encapsulant 2A alsoreduces the thermal resistance in the second resin encapsulant 2B.

Further, the second resin encapsulant 2B is required to have heatdissipation rather than moisture resistance. Thus, alumina, which has anexcellent thermal conductivity of 2.1 W/m·K, is used as the fillercontained in the second resin encapsulant 2B. Since the second resinencapsulant 2B contains alumina, the second resin encapsulant 2B becomesporous to exhibit high moisture absorption. However, this is notparticularly a problem because circuit elements, fine metal wires, andthe like are not disposed on the lower surface side and side surfaceside of the circuit board 4. It should be noted that as describedpreviously, as the filler contained in the second resin encapsulant 2B,crystalline silica, crushed silica, fused silica, or silicon nitride maybe used to be mixed with alumina.

As described previously, alumina, which has an excellent thermalconductivity, is used in the second resin encapsulant 2B. Alumina havinga polygonal shape such as crystalline alumina or crushed alumina isused. Accordingly, disposing the second resin encapsulant 2B such thatthe side surfaces of the circuit board 4 are covered as high as possibleunder conditions in which the second resin encapsulant 2B does not movearound to the upper surface side of the circuit board 4, solves theaforementioned problem of short circuits, and improves the heatdissipation of the circuit device 1. In other words, the range of theside surfaces of the circuit board 4 which is covered with the secondresin encapsulant 2B is adjusted in a range in which the moistureresistance of the upper surface side of the circuit board 4 can beensured.

It should be noted that though a description has been made in thisembodiment for the case where the resin sheet 13 placed under the lowersurface of the circuit board 4 is melted and thermally cured to form thesecond resin encapsulant 2B, the present invention is not limited tothis case. For example, similar to the first resin encapsulant 2A, thesecond resin encapsulant 2B may be formed by other manufacturing methodsuch as the injection of resin into a resin encapsulation mold orpotting. In other words, as described previously, it is enough to reducethe thermal resistance of the second resin encapsulant 2B and to improveheat dissipation from the lower surface side of the circuit board 4 andthe side surface side thereof. Other various modifications can be madewithout departing from the spirit of the present invention.

Next, a method of manufacturing a circuit device according to a secondembodiment of the present invention will be described. FIGS. 3A to 3Care cross-sectional views for explaining a state in which a circuitboard is placed in a resin encapsulation mold. FIGS. 4A and 4B arecross-sectional views for explaining a state in which resin is injectedinto the resin encapsulation mold. It should be noted that in thisembodiment, since a method of manufacturing the circuit device describedwith reference to FIGS. 1A to 2B will be described, the same componentsare denoted by the same reference numerals, and FIGS. 1A to 2B areappropriately referenced.

As shown in FIG. 3A, first, the circuit board 4 is prepared, and theinsulating layer 5 is formed on the circuit board 4. By attaching ametal film of, for example, copper to the upper surface of theinsulating layer 5 and etching the metal film into a desired pattern,the conductive pattern 6 and the pads 11 are formed on the circuit board4. Further, a large number of semiconductor elements 7 and chip elements8 are fixed at desired positions on the conductive pattern 6, and theleads 3 are fixed on the pads 11.

Next, the resin sheet 13 is mounted on the upper surface of the innerwall of the lower mold half 22 of the resin encapsulation mold 21, andthen the circuit board 4 is mounted on the upper surface of this resinsheet 13. Further, an upper mold half 23 and the lower mold half 22 arebrought into contact with each other to clamp the leads 3 between theupper and lower mold halves 23 and 22. Thus, the position of the circuitboard 4 is fixed in a cavity 24. It should be noted that at a stageprior to heat treatment after the placement in the resin encapsulationmold 21, the resin sheet 13 is in a solid state obtained by molding agranular thermosetting resin by compression molding as describedpreviously.

As shown in FIG. 3B, the thickness T3 of the resin sheet 13 is, forexample, approximately 0.8 mm. Thus, the resin sheet 13 is formed tohave a thickness larger than the thickness T1 (see FIG. 1B) of the resinencapsulant 2 covering the lower surface side of the circuit board 4 ofthe circuit device 1.

On the other hand, as described previously, the circuit board 4 in thecavity 24 comes into a state in which the leads 3 are clamped betweenthe upper and lower mold halves 23 and 22, and in which the position ofthe lower surface of the circuit board 4 is fixed at a positionseparated from the upper surface of the inner wall of the lower moldhalf 22 by T1. Accordingly, when the leads 3 are clamped by the resinencapsulation mold 21 in a state in which the circuit board 4 is mountedon the upper surface of the resin sheet 13, the leads 3 are elasticallydeformed as indicated by a circle 25. Further, the circuit board 4presses the resin sheet 13 against the lower mold half 22 to bring theresin sheet 13 into a fixed state.

As shown in FIG. 3C, the resin encapsulation mold 21 is equipped with aheater system (not shown), and the resin encapsulation mold 21 is heatedby the heater system to a temperature (e.g., 170° C. or higher) at whichthe resin sheet 13 is melted and thermally cured. Further, the positionsof the resin sheet 13 and the circuit board 4 are fixed in the cavity24, and then the resin encapsulation mold 21 is heated. Thus, the resinsheet 13 is melted and softened with the elapse of time.

As described previously, the leads 3 are clamped by the resinencapsulation mold 21 in an elastically deformed state. Accordingly,when the resin sheet 13 is melted, the leads 3 return to original shapesas indicated by a circle 26, and the circuit board 4 sinks into themelted resin. Further, with the sinking of the circuit board 4, themelted resin moves from a region under the circuit board 4 to a regionbeside the circuit board 4 to cure. Thus, the second resin encapsulant2B covers from the lower surface of the circuit board 4 to thevicinities of upper portions of the side surfaces thereof. At this time,the resin sheet 13 is formed to have a two-dimensional size larger thanthat of the circuit board 4. Accordingly, the second resin encapsulant2B reliably covers to the lower surface of the circuit board 4.Moreover, since the melted resin is moved from a region under thecircuit board 4 to a region beside the circuit board 4, the occurrenceof voids under the lower surface of the circuit board 4 is reduced.

As shown in FIG. 4A, a tablet 28 is dropped into a pod 27 provided inthe lower mold half 22 to be heated and melted, and then the tablet 28is pressed using a plunger 29. The tablet 28 is a product obtained bymolding a powdery thermosetting resin (epoxy resin, ortho-cresolnovolac/biphenyl, dicyclopentadiene, or the like) having an additivesuch as filler mixed therein into a columnar shape by compressionmolding. The resin encapsulation mold 21 is heated to approximately 170°C. or higher as described previously. Accordingly, when the tablet 28 isdropped into the pod 27, the tablet 28 is gradually melted. Further, thetablet 28 is melted into a liquid or semisolid state to flow through arunner 30 and pass through a gate 31, thus being supplied into thecavity 24.

As shown in FIG. 4B, the cavity 24 is filled with the resin obtained bythe melting of the tablet 28. At this time, since the temperature of theresin encapsulation mold 21 is higher than the temperature at which themelted resin is thermally cured, the resin filling the cavity 24polymerizes and cures with the elapse of time.

Here, in this step, for example, by adjusting the work sequence of thestep and the formulation of resins, the second resin encapsulant 2B isthermally cured before the first resin encapsulant 2A. Since this stepcauses the second resin encapsulant 2B to first cure integrally with thecircuit board 4, the circuit board 4 is prevented from being warped bythe shrinkage force produced when the first resin encapsulant 2A cures.Moreover, since the first resin encapsulant 2A is supplied into thecavity 24 in a liquid state, the thermal curing of the first resinencapsulant 2A proceeds under pressure from the plunger 29. As a result,as indicated by the circles 12, at a boundary surface between the firstresin encapsulant 2A and the second resin encapsulant 2B, pressure isapplied from the first resin encapsulant 2A to the side of the secondresin encapsulant 2B. This facilitates the polymerization of the resinencapsulants 2A and 2B, and improves the degree of integration thereof.Thus, moisture resistance in this polymerized region is ensured.

Finally, when the first resin encapsulant 2A and the second resinencapsulant 2B sufficiently polymerize and thermally cure in the resinencapsulation mold 21, the upper mold half 23 and the lower mold half 22are separated, and the circuit device 1 as a molded product is takenout. Then, portions of the cured resin which fill an air vent 32, therunner 30, and the like are cut off from the resin encapsulant 2, andouter lead portions of the leads are processed. Thus, the circuit deviceshown in FIGS. 1A and 1B is completed.

Next, a semiconductor device according to a third embodiment of thepresent invention will be described. FIG. 5B is a cross-sectional viewof a semiconductor device shown in FIG. 5A, which is taken along lineB-B. It should be noted that portions which are invisible due to thepresence of a resin encapsulant are also shown in FIG. 5A, and will bedescribed. Moreover, in the explanation thereof, the explanation ofFIGS. 1A to 2B will be appropriately taken into consideration.

As shown in FIG. 5A, a semiconductor device 41 mainly includes an island42, a semiconductor element 43 fixed on the island 42 with an adhesivesuch as solder, leads 46 electrically connected to electrode pads 44 ofthe semiconductor element 43 with fine metal wires 45, and a resinencapsulant 47 integrally covering the foregoing components. As shown inthe drawing, support leads 48 extend from four corners of the island 42outward. The island 42 is mechanically supported by these support leads48 to be continuous with a frame.

As shown in FIG. 5B, the resin encapsulant 47 includes a first resinencapsulant 47A and a second resin encapsulant 47B. In the drawingplane, a boundary between the first resin encapsulant 47A and the secondresin encapsulant 47B is drawn. However, in the actual semiconductordevice 41, the resin encapsulants 47A and 47B polymerize to beintegrated. Further, the first resin encapsulant 47A is formed byinjecting melted resin into the cavity of the resin encapsulation mold,and the second resin encapsulant 47B is formed by melting the resinsheet 13 (see FIG. 2A) placed under the lower surface of the island 42.The second resin encapsulant 47B has a thickness T4 of, for example, notless than 0.1 mm nor more than 0.3 mm to form a very thin film. Thus,thermal resistance in the second resin encapsulant 47B is reduced.

Further, the composition of the resin constituting the first resinencapsulant 47A is the same as that of the first resin encapsulant 2A,and the composition of the resin constituting the second resinencapsulant 47B is the same as that of the second resin encapsulant 2B.With regard to the explanation thereof, the explanation of FIGS. 1A to2B in the first embodiment will be taken into consideration, and theexplanation thereof will be omitted here. Further, as indicated by acircle 48, in the semiconductor device 41, also, the second resinencapsulant 47B covers from the lower surface of the island 42 to anupper portion of the side surfaces thereof. Further, since the secondresin encapsulant 47B under the lower surface of the island 42 is a thinfilm, the thermal resistance of the second resin encapsulant 47B isreduced. Thus, heat radiated from the semiconductor element 43 isfavorably radiated outside the semiconductor device 41 through theisland 42 and the second resin encapsulant 47B.

It should be noted that though a description has been made in thisembodiment for the case where the resin sheet 13 placed under the lowersurface of the island 42 is melted and thermally cured to form thesecond resin encapsulant 47B, the present invention is not limited tothis case. For example, similar to the first resin encapsulant 47A, thesecond resin encapsulant 47B may be formed by other manufacturing methodsuch as the injection of resin into a resin encapsulation mold orpotting. In other words, as described previously, it is enough to reducethe thermal resistance of the second resin encapsulant 47B and toimprove heat dissipation from the lower surface side of the island 42.Other various modifications can be made without departing from thespirit of the present invention.

Next, a method of manufacturing a semiconductor device according to afourth embodiment of the present invention will be described. FIGS. 6Aand 6B are plan views for explaining a die bonding step and a wirebonding step. FIGS. 7A to 7C are cross-sectional views for explaining astate in which a frame is placed in a resin encapsulation mold. FIGS. 8Aand 8B are cross-sectional views for explaining a state in which resinis injected into the resin encapsulation mold. It should be noted thatin this embodiment, since a method of manufacturing the semiconductordevice described with reference to FIGS. 5A and 5B will be described,the same components are denoted by the same reference numerals.Moreover, in the explanation thereof, the explanation of FIGS. 3A to 4Bwill be taken into consideration.

As shown in FIG. 6A, first, a lead frame 51 having a predetermined shapeis prepared. The lead frame 51 is made of a metal plate of copper or thelike having a thickness of, for example, approximately 0.3 mm, and isformed into a predetermined shape by etching or press working. Further,the lead frame 51 has the shape of a strip as a whole, and a pluralityof collective blocks 52 indicated by dotted lines are disposed in thelongitudinal direction of the lead frame 51. In each of the collectiveblocks 52, a plurality of mount portions 53 are formed.

As shown in FIG. 6B, in the collective block 52, connecting portions 54and 55 extend in the faun of a grid in the horizontal and verticaldirections, and a mount portion 53 is formed in each of regionssurrounded by the connecting portions 54 and 55 as indicated by a dottedline. Further, for each of the mount portions 53, the semiconductorelement 43 is fixed on the island 42 with an adhesive, and the electrodepads 44 of the semiconductor element 43 and the leads 46 areelectrically connected to each other with the fine metal wires 45.

As shown in FIG. 7A, the resin sheet 13 is mounted on the upper surfaceof the inner wall of a lower mold half 57 of a resin encapsulation mold56, and then the island 42 is mounted on the upper surface of this resinsheet 13. Further, an upper mold half 58 and the lower mold half 57 arebrought into contact with each other to place the mount portion 53 (seeFIG. 6B) including the island 42 in a cavity 59. As shown in thedrawing, the support leads 48 are clamped between the upper and lowermold halves 58 and 57. Thus, the position of the island 42 in the cavity59 is fixed. It should be noted that at a stage prior to heat treatmentafter the placement in the resin encapsulation mold 56, as describedpreviously, the resin sheet 13 is in a solid state obtained by molding agranular thermosetting resin by compression molding as describedpreviously.

As shown in FIG. 7B, the thickness T3 of the resin sheet 13 is, forexample, approximately 0.8 mm. Thus, the resin sheet 13 is formed tohave a thickness larger than the thickness T4 (see FIG. 7C) of the resinencapsulant 47 covering the lower surface side of the island 42.

On the other hand, as described previously, the island 42 in the cavity59 comes into the state in which the support leads 48 are clampedbetween the upper and lower mold halves 58 and 57, and in which theposition of the lower surface of the island 42 is fixed at a positionseparated from the upper surface of the inner wall of the lower moldhalf 57 by T3. Accordingly, when the support leads 48 are clamped by theresin encapsulation mold 56 in a state in which the island 42 is mountedon the upper surface of the resin sheet 13, the support leads 48 areelastically deformed, and the resin sheet 13 is fixed in place in thestate of being pressed against the lower mold half 57 by the island 42.It should be noted that dotted lines indicate a state in which thesupport leads 48 are not deformed.

As shown in FIG. 7C, the resin encapsulation mold 56 is equipped with aheater system (not shown), and the resin encapsulation mold 56 is heatedby the heater system to a temperature (e.g., 170° C. or higher) at whichthe resin sheet 13 is melted and thermally cured. Further, the positionsof the resin sheet 13 and the island 42 are fixed in the cavity 59, andthen the resin encapsulation mold 56 is heated. Thus, the resin sheet 13is melted and softened with the elapse of time, and the lower surface ofthe island 42 is covered with the melted resin. It should be noted thatthe second resin encapsulant 47B has a thickness T4 of, for example, notless than 0.1 mm nor more than 0.3 mm to form a very thin film, and thatthe thermal resistance in the second resin encapsulant 47B is reduced.

As shown in the drawing, when the resin sheet 13 is melted, the supportleads 48 return to original shapes, and the island 42 sinks downward.Further, with the sinking of the island 42, part of the melted resinmoves from a region under the island 42 to a region beside the island42, and the second resin encapsulant 47B covers from the lower surfaceof the island 42 to upper portions of the side surfaces thereof.

As shown in FIG. 8A, a tablet 61 is dropped into a pod 60 provided inthe lower mold half 57 to be heated and melted, and then the tablet 61is pressed using a plunger 62. The tablet 61 is a product obtained bymolding a powdery thermosetting resin (epoxy resin, ortho-cresolnovolac/biphenyl, dicyclopentadiene, or the like) having an additivesuch as filler mixed therein into a columnar shape by compressionmolding. The resin encapsulation mold 56 is heated to approximately 170°C. or higher as described previously. Accordingly, when the tablet 61 isdropped into the pod 60, the tablet 61 is gradually melted. Further, thetablet 61 is melted into a liquid or semisolid state to flow through arunner 63 and pass through a gate 64, thus being supplied into thecavity 59.

As shown in FIG. 8B, the cavity 59 is filled with the resin obtained bythe melting of the tablet 61. At this time, since the temperature of theresin encapsulation mold 56 is higher than the temperature at which themelted resin is thermally cured, the resin filling the cavity 24polymerize and cure with the elapse of time. It should be noted that asdescribed with reference to FIG. 4B previously, the boundary surfacebetween the first resin encapsulant 47A and the second resin encapsulant47B polymerizes to integrally cure.

Finally, when the first resin encapsulant 47A and the second resinencapsulant 47B sufficiently polymerize and thermally cure in the resinencapsulation mold 56, the upper mold half 58 and the lower mold half 57are separated, and the semiconductor device 41 as a molded product istaken out. Then, portions of the cured resin which fill an air vent 65,the runner 63, and the like are cut off from the resin encapsulant 47,and outer lead portions of the leads are processed. Thus, thesemiconductor device shown in FIG. 5A is completed.

In the preferred embodiments, the resin encapsulant includes two typesof encapsulating resins, and the polymerized region of the encapsulatingresins is located on the side surfaces of the circuit board. Thus, thewithstand voltage characteristic is improved, and the circuit board isprevented from being short-circuited.

Moreover, in the preferred embodiments, the particle size of the fillerof the encapsulating resin covering from the lower surface side of thecircuit board to the upper portion of the side surfaces thereof islarger than the particle size of the filler of the encapsulating resincovering the upper surface side of the circuit board. Thus, heatdissipation to the outside of the circuit device is improved.

Moreover, in the preferred embodiments, the structure is employed inwhich circuit elements and the like are not disposed on the lowersurface side of the circuit board, and alumina is used as the filler inthe resin on the lower surface side of the circuit board. Thus, thethermal resistance of the resin containing the filler is greatlyreduced.

Moreover, in the preferred embodiments, the resin on the lower surfaceside of the circuit board is formed by using the resin sheet. Thus, theparticle size of the filler contained in the resin becomes large, andheat dissipation to the outside of the circuit device is improved.

Moreover, in the preferred embodiments, the shape of the filler disposedon the lower surface side of the circuit board is the polygonal shape.Thus, the thermal resistance of the resin containing the filler isgreatly reduced.

Moreover, in the preferred embodiments, silica is used as the filler inthe resin on the upper surface side of the circuit board in whichimportance is placed on moisture resistance. Thus, materials cost isgreatly reduced.

Moreover, in the preferred embodiments, the encapsulating resin coveringfrom the lower surface side of the circuit board to the upper portion ofthe side surface thereof is cured before the encapsulating resincovering the upper surface side of the circuit board. Thus, the warpageof the circuit board can be prevented.

What is claimed is:
 1. A circuit device comprising: a circuit boardhaving a first main surface, a second main surface opposite from thefirst main surface and a side surface connecting the first and secondmain surfaces; a conductive pattern disposed on the first main surfaceof the circuit board; a circuit element disposed on the conductivepattern; and a resin encapsulant covering the circuit board andcomprising a first resin encapsulant covering at least the first mainsurface of the circuit board and part of the side surface of the circuitboard and a second resin encapsulant covering at least the second mainsurface of the circuit board and part of the side surface of the circuitboard, wherein a polymerized region of the first resin encapsulant andthe second resin encapsulant is formed beside the side surface of thecircuit board, and the polymerized region is located closer to the firstmain surface than to the second main surface so that a top portion ofthe polymerized region is located at a position lower than the firstmain surface of the circuit board.
 2. The circuit device according toclaim 1, wherein a particle size of filler contained in the second resinencapsulant is larger than a particle size of filler contained in thefirst resin encapsulant.
 3. The circuit device according to claim 2,wherein material properties of the filler contained in the second resinencapsulant is different from material properties of the fillercontained in the first resin encapsulant, and a thermal conductivity ofthe filler contained in the second resin encapsulant is larger than athermal conductivity of the filler contained in the first resinencapsulant.
 4. The circuit device according to any one of claims 2 or3, wherein the second resin encapsulant is made of a resin obtained bymelting and curing a resin sheet formed by pressing a powdered resin anddisposed under the second main surface of the circuit board.
 5. Thecircuit device according to claim 2, wherein a shape of the fillercontained in the second resin encapsulant is any one of a crystallineshape and a crushed shape.
 6. The circuit device according to claim 3,wherein a shape of the filler contained in the second resin encapsulantis any one of a crystalline shape and a crushed shape.
 7. The circuitdevice according to claim 2, wherein the filler contained in the firstresin encapsulant is spherical silica, and the filler contained in thesecond resin encapsulant is alumina.
 8. The circuit device according toclaim 3, wherein the filler contained in the first resin encapsulant isspherical silica, and the filler contained in the second resinencapsulant is alumina.
 9. The circuit device according to claim 4,wherein the filler contained in the first resin encapsulant is sphericalsilica, and the filler contained in the second resin encapsulant isalumina.
 10. The circuit device according to claim 5, wherein the fillercontained in the first resin encapsulant is spherical silica, and thefiller contained in the second resin encapsulant is alumina.
 11. Thecircuit device according to claim 1, wherein the circuit board comprisesa substrate and an insulating layer disposed on the substrate, and theconductive pattern is disposed on the insulating layer.